1. Field of the Invention
This invention relates to the field of radiation manipulation. In particular, the invention relates a method and apparatus for altering a beam of light or radiant energy.
2. Description of Related Art
Heretofore, light has been manipulated to produce an alignment field with laser based equipment as shown in U.S. Pat. No. 3,588,249 where a collimated laser beam is rotated 360 degrees about an axis to establish an alignment plane. Remote receivers in the vicinity may detect the laser beam as it sweeps past, and provide a visual or audible indication when they are aligned in the laser plane. While this rotating beacon technique provides results that are quite useful over long ranges, the cost of the mechanical and optical structures for implementing the technique with the desired amount of accuracy is relatively high. Also, the plane is more difficult to locate if the receiver is moved through the plane before the beam strikes its detector.
An improvement is disclosed in U.S. Pat. No. 4,674,870 that includes a laser alignment system employing a transmitter and one or more receivers. The transmitter produces an alignment field by projecting laser energy in a non-planar reference cone, and the receivers locate this reference cone with photodetectors. The laser energy in the alignment field is modulated at 8 kHz and the signals produced by the photodetectors are filtered and amplified to increase the range of the system. Each receiver operates a display, which indicates when it is aligned in the reference cone, and it produces an out-of-level indication when the transmitter is not properly aligned.
A transmitter for an alignment system is shown in U.S. Pat. No. 4,679,937 in which a field of electromagnetic radiation is propagated in a non-planar reference cone. The transmitter includes a source for providing a collimated beam of electromagnetic radiation directed parallel to a beam axis. A cantilever strand supports a bob within the beam. The bob has a conical reflection surface to reflect the collimated beam conically. Optimally, the cantilever stand and bob are chosen to provide a deflection between the bob and plumb which is substantially one-half of any angular error between the beam axis and plumb. In a preferred form, a housing surrounds the bob and has inner and outer surfaces, which minimize temperature effects on the orientation of the reference plane. In addition, detectors are provided to sense when the angular error between the beam axis and plumb is outside of an acceptable range. Other leveling devices are shown in U.S. Pat. Nos. 5,914,778; 5,940,557; 5,994,688; 6,005,719 and 6,009,630.
Obviously, in view of the above prior art, there is still a need for a cost effective level line system.